Repeater Defect Detection

ABSTRACT

Defects from a hot scan can be saved, such as on persistent storage, random access memory, or a split database. The persistent storage can be patch-based virtual inspector virtual analyzer (VIVA) or local storage. Repeater defect detection jobs can determined and the wafer can be inspected based on the repeater defect detection jobs. Repeater defects can be analyzed and corresponding defect records to the repeater defects can be read from the persistent storage. These results may be returned to the high level defect detection controller.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to the provisional patent applicationsassigned U.S. App. No. 62/515,445 and U.S. App. No. 62/515,449, bothfiled Jun. 5, 2017, the disclosures of which are hereby incorporated byreference.

FIELD OF THE DISCLOSURE

This disclosure relates to inspection of semiconductor wafers.

BACKGROUND OF THE DISCLOSURE

Evolution of the semiconductor manufacturing industry is placing evergreater demands on yield management and, in particular, on metrology andinspection systems. Critical dimensions are shrinking while wafer sizeis increasing. Economics is driving the industry to decrease the timefor achieving high-yield, high-value production. Thus, minimizing thetotal time from detecting a yield problem to fixing it determines thereturn-on-investment for the semiconductor manufacturer.

Fabricating semiconductor devices, such as logic and memory devices,typically includes processing a semiconductor wafer using a large numberof fabrication processes to form various features and multiple levels ofthe semiconductor devices. For example, lithography is a semiconductorfabrication process that involves transferring a pattern from a reticleto a photoresist arranged on a semiconductor wafer. Additional examplesof semiconductor fabrication processes include, but are not limited to,chemical-mechanical polishing (CMP), etch, deposition, and ionimplantation. Multiple semiconductor devices may be fabricated in anarrangement on a single semiconductor wafer and then separated intoindividual semiconductor devices.

Extreme ultraviolet (EUV) lithography increases the need for robustdetection of repeater defects. There are no actinic light maskinspectors for EUV. Thus, the task of mask inspection shifts frommask-inspectors to wafer-inspectors. The frequency of in-line maskinspections can be rather high since there is no pellicle for EUV masksand the masks are exposed during operation.

Defect review for advanced design rules can be for objects that arequite small (e.g., for detection of defects below 10 nm), so hot scansmay be run to catch such defects. A “hot scan” generally refers to ameasurement/inspection of a wafer performed to detect defects or takemeasurements on the wafer by applying relatively aggressive detectionsettings (e.g., thresholds substantially close to the noise floor). Inthis manner, the hot scan may be performed to collect inspection ormeasurement data about the wafer that will be used for the tuningprocess (optics selection and algorithm tuning). The goal of the hotscan may be to detect a representative sample of all defect and nuisancetypes on the wafer in the selected mode(s).

Repeater detection (e.g., with coordinates matching) can be a strongfilter that can bring the nuisance density to manageable levels.However, a repeater defect detection (RDD) algorithm is typicallyperformed as the last inspection step and requires all defects to becollected in the final lot result. Hot inspections required for maskqualification may result in millions of defect candidates prior to RDD.This can cause tool choking and dropped defects when transferringresults from the inspection system to the high level defect detectioncontroller. RDD may be subject of the same limitations of maximum numberof defects and defects density as random defect detection inspection,although the final number of defects of interest (DOIs), such asrepeaters, may be reasonably small. It should be noted that manyrepeater defects are “soft” repeaters. Soft repeaters are not printed inevery reticle due to process variation. This means that it may not bepossible to use in-job RDD while being able to analyze results for thewhole wafer.

With feature shrink and a potential resolution limit for optical waferinspection tools, the primary candidate inspection tool for print checkis an electron beam inspection tool, such as a scanning electronmicroscope (SEM). However, electron beam inspection tools have athroughput disadvantage. With the best scenario of multiple beam/columnoptions, the estimated inspection time for one reticle is more than 8hours. Broad band plasma (BBP) tools have much higher throughput and,hence, coverage. In the current BBP tool design, repeater analysis ispart of the post-processing step in the high level defect detectioncontroller. Due to architecture limitations (both software andhardware), there may be a limit of less than 10 million defects thatresult using current BBP tool configurations. However, estimations showthat about 10 billion defects may need to be handled. Optimization ofthroughput and development time is a serious challenge for RDD.

Furthermore, current inspections are performed using die-to-diecomparisons and show high levels of nuisance due to design systematicnuisance events. These nuisance events can be real defects, but areknown to be non-critical defects. Detection of DOI can be impairedbecause there are too many systematic nuisance events.

Therefore, improved RDD is needed.

BRIEF SUMMARY OF THE DISCLOSURE

In a first embodiment, a method to detect repeater defects is disclosed.The method includes performing a hot scan inspection of an entiresurface of a wafer. A position of defects from the hot scan inspectionis stored to a storage medium. The storage medium is persistent storage,random access memory, or a split database. Using a processor,coordinates for repeater defect detection are determined. The wafer isinspected based on the coordinates for repeater defect detection.Repeater defects are analyzed using the processor. Corresponding defectrecords to the repeater defects are retrieved from the storage medium.

A patch-based virtual inspector virtual analyzer or local storage can beused for the storage medium

The method can further include freeing space in the storage medium afterthe retrieving.

The method can further include saving coordinates of the defects inshared memory prior to the determining.

In an instance, a first die and a second die are each imaged using areticle at two different positions on a first wafer and two differentpositions on a second wafer. In this instance, the method includescalculating a first wafer difference image in a first wafer step andcalculating a second wafer difference image in a second wafer step.Calculating the first wafer difference image in the first wafer stepincludes calculating, using the processor, a difference image of thefirst die and the second die at a second position on the first wafer.Using the processor, a difference image of the first die at the secondposition on the first wafer and the second die at a first position onthe first wafer is calculated. Using the processor, the first waferdifference image of the two difference images of the first wafer step iscalculated.

Calculating a second wafer difference image in a second wafer stepincludes calculating, using the processor, a difference image of thefirst die and the second die at a second position on the second wafer.Using the processor, a difference image of the first die at the secondposition on the first wafer and the second die at a first position onthe second wafer is calculated. Using the processor, the second waferdifference image of the two difference images of the second wafer stepis calculated.

Using the processor, systematic defects can be found in the first waferdifference image using coordinate-based defect source analysis. Usingthe processor, the systematic defects in the first wafer differenceimage can be subtracted from the second wafer difference image. Usingthe processor, existence of a defect of interest in the second waferdifference image can be determined after the subtracting.

In an instance, a first die and a second die are each imaged using areticle at two different positions on a first wafer and two differentpositions on a second wafer. In this instance, the method includescalculating a first wafer difference image in a first wafer step andcalculating a second wafer difference image in a second wafer step.Calculating a first wafer difference image in a first wafer stepincludes calculating, using the processor, a difference image of thefirst die and the second die at a second position on the first wafer.Using the processor, a difference image of the first die at the secondposition on the first wafer and the second die at a first position onthe first wafer is calculated. Using the processor, the first waferdifference image of the two difference images of the first wafer step iscalculated.

Calculating a second wafer difference image in a second wafer stepincludes calculating, using the processor, a difference image of thefirst die and the second die at a second position on the second wafer.Using the processor, a difference image of the first die at the secondposition on the first wafer and the second die at a first position onthe second wafer is calculated. Using the processor, the second waferdifference image of the two difference images of the second wafer stepis calculated.

Using the processor, the second wafer difference image is subtractedfrom the first wafer difference image. Using the processor, existence ofa defect of interest in the second wafer difference image is determinedafter the subtracting.

In an instance, a first die and a second die are each imaged using areticle at two different positions on a first wafer and two differentpositions on a second wafer. In this instance, a wafer difference imageis calculated, which includes calculating, using the processor, adifference image of the first die and the second die at a secondposition on the second wafer; calculating, using the processor, adifference image of the first die at the second position on the firstwafer and the second die at a first position on the second wafer; andcalculating, using the processor, the wafer difference image of the tworesulting difference images. Using the processor, existence of a defectof interest in the wafer difference image is determined. Images areretrieved from the storage medium. The images are at a same location onthe first wafer as the first die and the second die on the second wafer.Using the processor, presence of the defect of interest is evaluated inthe images from the storage medium. Using the processor, nuisance isfiltered from the wafer difference image.

In a second embodiment, a method for filtering nuisance is provided. Themethod comprises imaging a first die and a second die using a reticle attwo different positions on a first wafer and two different positions ona second wafer. A difference image of the second wafer in a second waferstep is calculated by: calculating, using a processor, a differenceimage of the first die and the second die at a second position on thesecond wafer; calculating, using the processor, a difference image ofthe first die at the second position on the first wafer and the seconddie at a first position on the second wafer; and calculating, using theprocessor, the difference image of the second wafer using the twodifference images of the second wafer step. Using the processor,existence of a defect of interest in the wafer difference image of thesecond wafer is determined.

The method can further comprise retrieving images from the storagemedium. The images are at a same location on the first wafer as thefirst die and the second die on the second wafer. Using the processor,presence of the defect of interest in the images from the storage mediumis evaluated. Using the processor, nuisance is filtered from the secondwafer difference image.

The method can further comprise calculating a difference image of thefirst wafer in a first wafer step. Calculating a difference image of thefirst wafer in a first wafer step includes calculating, using theprocessor, a difference image of the first die and the second die at asecond position on the first wafer. Using the processor, a differenceimage of the first die at the second position on the first wafer and thesecond die at a first position on the first wafer is calculated. Usingthe processor, the wafer difference image of the first wafer using thetwo difference images of the first wafer step is calculated. Using theprocessor, systematic defects in the difference image of the first waferare found using coordinate-based defect source analysis. Using theprocessor, the systematic defects in the difference image of the firstwafer are subtracted from the difference image of the second wafer.Determining existence of the defect of interest in the difference imageof the second wafer is after the subtracting.

The method can further comprise calculating a difference image of thefirst wafer in a first wafer step. Calculating a difference image of thefirst wafer in a first wafer step includes calculating, using theprocessor, a difference image of the first die and the second die at asecond position on the first wafer. Using the processor, a differenceimage of the first die at the second position on the first wafer and thesecond die at a first position on the first wafer is calculated. Usingthe processor, the difference image of the first wafer using the twodifference images of the first wafer step is calculated. Using theprocessor, the difference image of the second wafer is subtracted fromthe difference image of the first wafer. Determining existence of thedefect of interest in the difference image of the second wafer is afterthe subtracting.

In a third embodiment, a system is provided. The system comprises acontroller in electronic communication with a wafer inspection tool. Thecontroller includes a processor and an electronic data storage unit inelectronic communication with the processor. The electronic data storageunit includes persistent storage, random access memory, or a splitdatabase. The controller is configured to: receive results of a hot scaninspection of an entire surface of a wafer from the wafer inspectiontool; store a position of defects from the hot scan inspection to theelectronic data storage unit; determine coordinates for repeater defectdetection; send instructions to inspect the wafer based on thecoordinates for repeater defect detection; analyze repeater defects; andretrieve corresponding defect records to the repeater defects from theelectronic data storage unit.

The electronic data storage unit may be included in a patch-basedvirtual inspector virtual analyzer. The electronic data storage unitalso may be local storage.

The controller may be configured to save coordinates of the defects inshared memory prior to determine the repeater defect detection jobs.

In an instance, a first die and a second die are each imaged using areticle at two different positions on a first wafer and two differentpositions on a second wafer. The controller is further configured tocalculate a first wafer difference image in a first wafer step andcalculate a second wafer difference image in a second wafer step.Calculating a first wafer difference image in a first wafer stepincludes: calculating a difference image of the first die and the seconddie at a second position on the first wafer; calculating a differenceimage of the first die at the second position on the first wafer and thesecond die at a first position on the first wafer; and calculating thefirst wafer difference image of the resulting difference images of thefirst wafer step. Calculating a second wafer difference image in asecond wafer step includes: calculating a difference image of the firstdie and the second die at a second position on the second wafer;calculating a difference image of the first die at the second positionon the first wafer and the second die at a first position on the secondwafer; and calculating the second wafer difference image of theresulting difference images of the second wafer step. Systematic defectsin the first wafer difference image are found using coordinate-baseddefect source analysis. The systematic defects in the first waferdifference image are subtracted from the second wafer difference image.Existence of a defect of interest in the second wafer difference imageis determined after the subtracting.

In an instance, a first die and a second die are each imaged using areticle at two different positions on a first wafer and two differentpositions on a second wafer. The controller is further configured tocalculate a first wafer difference image in a first wafer step andcalculate a second wafer difference image in a second wafer step.Calculating a first wafer difference image in a first wafer stepincludes: calculating a difference image of the first die and the seconddie at a second position on the first wafer; calculating a differenceimage of the first die at the second position on the first wafer and thesecond die at a first position on the first wafer; and calculating thefirst wafer difference image of the resulting difference images of thefirst wafer step. Calculating a second wafer difference image in asecond wafer step includes: calculating a difference image of the firstdie and the second die at a second position on the second wafer;calculating a difference image of the first die at the second positionon the first wafer and the second die at a first position on the secondwafer; and calculating the second wafer difference image of theresulting difference images of the second wafer step. The second waferdifference image is subtracted from the first wafer difference image.Existence of a defect of interest in the second wafer difference imageis determined after the subtracting.

In an instance, a first die and a second die are each imaged using areticle at two different positions on a first wafer and two differentpositions on a second wafer. The controller is further configured tocalculate a wafer difference image. Calculating the wafer differenceimage includes: calculating a difference image of the first die and thesecond die at a second position on the second wafer; calculating adifference image of the first die at the second position on the firstwafer and the second die at a first position on the second wafer; andcalculating the wafer difference image of the resulting differenceimages. Existence of a defect of interest in the second wafer differenceimage is determined. Images are retrieved from the electronic datastorage unit. The images are at a same location on the first wafer asthe first die and the second die on the second wafer. Presence of thedefect of interest in the images from the electronic data storage unitis evaluated. Nuisance is filtered from the wafer difference image.

DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and objects of the disclosure,reference should be made to the following detailed description taken inconjunction with the accompanying drawings, in which:

FIG. 1 is an embodiment of a method in accordance with the presentdisclosure;

FIG. 2 is a block diagram of a system in accordance with the presentdisclosure;

FIG. 3 is a first embodiment of nuisance reduction in accordance withthe present disclosure;

FIG. 4 is a second embodiment of nuisance reduction in accordance withthe present disclosure;

FIG. 5 is a third embodiment of nuisance reduction in accordance withthe present disclosure; and

FIGS. 6-9 are variations of the embodiment of the method illustrated inFIG. 1.

DETAILED DESCRIPTION OF THE DISCLOSURE

Although claimed subject matter will be described in terms of certainembodiments, other embodiments, including embodiments that do notprovide all of the benefits and features set forth herein, are alsowithin the scope of this disclosure. Various structural, logical,process step, and electronic changes may be made without departing fromthe scope of the disclosure. Accordingly, the scope of the disclosure isdefined only by reference to the appended claims.

RDD can overcome the previous limitations. The mechanisms disclosedherein are based on the high accuracy of the defect location to performRDD at, for example, better than ±0.5 pixel. Repeater coordinates can bea strong filter that will suppress a majority of the random defects in ahot inspection, which can enable use of lower thresholds. Repeaters maybe detectable by at least one defect detection algorithm. If the defectis deep in the noise floor, then the problem shifts from RDD into normaldefect detection space.

Patch images and attributes can help with nuisance reduction. However,having patches and/or attributes for a final lot result may involvekeeping patches and attributes of all events before RDD. The size oftotal patches from 10 billion defects likely will not fit into memory.Furthermore, writing patches for all detected events before RDD tostorage and retrieving patches for detected repeaters from storage takestime on an inspection tool.

The embodiments disclosed herein take advantage of a storage medium,such as virtual inspector virtual analyzer (VIVA) storage, which may bein a separate tool or system from the inspection system. This can avoidthe throughput challenge of writing or reading to disk. Patches andattributes can be kept for set up only. Attributes can be limited and nopatches may be used for production.

There are several techniques to achieve high defect density forcandidate defects disclosed herein.

FIG. 1 is an embodiment of a method 100 to detect repeater defects. Thiscan use a split database such that coordinates can be saved in the imagecomputer (IMC) of the inspection tool and attributes can be saved on thesolid state drive (SSD), such as an SSD included in the IMC. At 101, ahot scan inspection of an entire surface of a wafer is performed, suchas using a BBP tool, a laser scanning tool, an electron beam inspector,or other inspection systems. At 102, positions of defects from the hotscan inspection are stored to a storage medium, such as persistentstorage, random access memory (RAM), or a split database. The persistentstorage can be patch-based VIVA or local (e.g., on the node) storage.Both might be a hybrid hard drive (HDD) or SSD. Patch-based VIVA orlocal storage can be used for the persistent storage.

At 103, coordinates for RDD (e.g., the RDD jobs) are determined, such asusing a processor. The wafer is inspected based on the coordinates forRDD at 104. Repeater defects are analyzed at 105. Corresponding defectrecords to the repeater defects are retrieved from the persistentstorage at 106. These may be returned to the high level defect detectioncontroller.

The method 100 can further include freeing space in the persistentstorage after the retrieving.

The method 100 can further include saving coordinates of the defects inshared memory prior to the determining at 103.

The method 100 is based on RDD usually requiring only defectcoordinates. Neither patches nor attributes are necessary because theRDD algorithm uses defect coordinates based on a definition of arepeater defect. Additional filtering based on attributes and/or patchescan be done as a separate step before or after RDD. This means that adefect structure can be saved for every defect candidate on VIVA or onthe local node redundant array of independent disks (RAID) and defectcoordinates can be kept in the shared memory. This reduces the size ofthe defect structure used for RDD to bounding box coordinates (e.g.,four integers) and die row, swath in a die-row, frame number, or otherfeatures. The whole defect may take only eight integers in shared memorybuffer. Up to 1,900 defects per frame can be kept without increase ofthe installed dynamic random-access memory (DRAM). After the RDD isperformed, the corresponding patches and defect attributes can beuploaded from the storage. This can be sent to the high level defectdetection controller or other controllers.

Variations of the method 100 are illustrated in FIGS. 6-9. FIGS. 6-9 aredifferent ways to realize the sequence described by FIG. 1 and providedifferent trade-offs between speed and the amount of details available.FIGS. 6-9 also demonstrate that RDD inspection setup can be performedeither on VIVA or on the inspection tool, which can be a compromisebetween tool utilization and necessity to have additional hardware, suchas VIVA.

Data storage can be freed immediately after inspection. It may bepossible to achieve 0.6 GB/s per node writing speed. This translatesinto 5,000 seconds (approximately 84 minutes) to save 3 TB of data thatmay be needed for 300 defect candidates per frame. This input/output canwork in parallel with data processing, which will increase throughput.Bandwidth can be doubled with SSD and inspection time can be reduced.

The embodiment can provide a comprehensive solution for RDD of weakdefects and soft repeaters. The change of the architecture that may beneeded for RDD of weak defects may be reused for other applications.

In an instance, two-pass RDD is performed based on IMC. A first passdoes not report anything to the user interface and saves coordinates inthe IMC memory. A second pass reads coordinates, extracts patches, andcomputes attributes for repeaters only. This can balance hardware costswith a throughput reduction, which may be suitable for prototypedevelopment.

RDD jobs or other coordinates for RDD can save defect coordinates inshared memory and skip patch extraction and defect attributescalculation. After wafer swathing is done, RDD jobs that can findrepeaters among the saved defect candidates are issued. The repeatercoordinates can be returned to a controller and/or the high level defectdetection controller. Defect images and attributes can be extracted fromthese locations. Defect patches and defect attributes can be returnedfor repeater locations.

For prototyping, results based on the coordinates for RDD can be savedin the shared memory and normal defect detection jobs can be used forthe second pass. Corresponding files with repeater coordinates can beread and either defect detection jobs are converted into SRI ones or anempty result buffer is returned.

In another instance, job level repeaters detection is performed. Thiscan increase a job size to cover a full length of a die row.Frame-to-frame alignment can be precise and accurate inside one job, soit may be possible to do repeater detection as post-processing withtight tolerances (e.g., smaller than pixel). The job size is increasedto a full die row. Not all dies may be used for feature image (median)computation. For example, twelve frames may be sufficient for featureimage computation. Only die repeaters will be returned and furtherrepeater analysis will be performed by the high level defect detectioncontroller to suppress die repeaters and keep reticle repeaters. Thiscan provide relatively high throughput.

In another instance, a patch-based VIVA approach is used. All defectcandidates can be saved on the patch-based VIVA. A special applicationcan run RDD on defect candidate patches and attributes instead of fullwafer images. This can provide relatively high throughput.

All defect candidates can be saved on the patch-based VIVA. VIVAcapacity may be approximately ten defects per frame for fifteen planeinspection, so 150 defects per frame can likely be handled with a singleplane version. There may be no need to keep these defect candidates forany significant amount of time. Candidates from one inspection can berecorded, processed, and the data can be removed. This can enable hotterinspections. With high defect density, the whole wafer image can besaved on VIVA while defect coordinates are kept in the paralleldatabase. RDD may only need coordinates and defect patches can beextracted later for repeaters only.

During operation, hot inspections are run and all defect candidates aresaved on VIVA. The tool is then available for next inspection. On theVIVA, a new inspection type for RDD is initialized, repeaters are foundusing defect coordinates, and these are saved as part of patch records.Defect locations, attributes, and patches are then returned to the highlevel defect detection controller. These defect locations, attributes,and patches may have already been calculated and pre-saved on VIVA.

In another instance, a special swath layout approach is used. The sameswath can be scanned in every die row, the process can return to aninitial point, and the next swath can be scanned. The number of defectssaved by the high level defect detection controller can be reduced bychanging the swathing sequence. Instead of swathing every die-rowsequentially, every first swath can be swathed for every die-row, alldefects can be reported, and then every second swath for every die-rowis swathed. This process can be repeated. In an example, up to fourswaths are performed in every die-row. Four columns may be workindependently in this example. The controller receives results, canperform inter-job and inter-sub-swath merging before sending defects tothe high level defect detection controller. The high level defectdetection controller can run RDD with zero pixel coordinate tolerance.

Alternatively, all defects can be reported to the high level defectdetection controller that will run RDD prior to saving defects to thedisk.

In another instance, an IMC-based RDD is used. All defect candidates maybe kept in the IMC memory. Thus, the biggest portion of the RDD is donein the IMC.

All defect candidates can be accumulated in the IMC memory up to the endof wafer inspection. Normal defect detection can be run and a return ofa “no defects” result can buffer to the controller. All defectcandidates can be saved in the shared memory.

For example, assume that the system is using two columns and six nodesper column and the size of the defect structure(s) is about 10 KB. If120,000,000 defect candidates per wafer are desired, then 10,000,000defects per node may need to be kept in shared memory. This translatesinto 100,000,000,000 bytes or about 100 GB of shared memory per node.For a 300 mm wafer and 50 nm pixel size, an inspection can contain about28,260,000 frames. Without patches, 200 defects per frame can beachieved. If the node memory is increased to 1 TB, approximately 50 to60 defect candidates per frame can be handled. An SSD can be used atevery node rather than increasing the amount of DRAM.

After defect detection is done and all defect candidates are in theshared memory, a controller can either spawn a new process or submit newjobs (e.g., of new job type). Inter-job defects merge can be performedand RDD can be performed using the defect candidates available. Sincethe data in the shared memory can be organized by swath-sub-swathnumber, load balancing can be done by assigning swath-sub-swath numberto process to CPU core. After the RDD is done, repeaters can be returnedin a result buffer.

Defect candidate density can be increased by an order of magnitude(e.g., 90 defects per frame) if defect patches are dropped and the sizeof the defect structure is reduced, such as to about 1 KB.

In another instance, a special swath layout is combined with IMC-basedRDD. This can reduce IMC memory requirements. This technique enablesextreme defect candidate density and improved sensitivity.

Defect candidates detection can be performed for every first swath(i.e., every two swaths taking columns into account) for all die-rowskeeping all defect candidates in the node shared memory. RDD can beperformed for these candidates. Results can be returned to thecontroller and high level defect detection controller without collectingthe data for the rest of the wafer. The whole shared memory can be usedfor this small part of the wafer. Defect candidates density can beincreased proportionally.

For example, the longest swath on the 300 mm wafer and 50 nm pixel isabout 6,000 frames per swath and 120,000 frames per swath-die-row(assuming 20 die-rows on a wafer). For 100 GB shared memory, this canhandle 10,000,000 defects per swath or 83 defects per frame. For shorterswaths defect density can be higher and may be 160 defects per frame onaverage.

Swathing can be optimized for throughput and to reduce number ofY-motions for shorter swaths.

If the node memory is increased to 512 GB and 400 GB is used for defectstorage shared memory, then about 350 defects per frame can be saved.

This technique can be run hotter and may reach 1,600 defects per framewithout defect patches. However, instead of collecting two swaths perdie-row, twelve swath per die row can be performed to cover the wholewafer in four sets of swaths.

In an embodiment, soft repeaters can be identified and nuisance inrepeater defect images can be reduced. Repeater defects can include bothhard repeaters (which are always visible on a die) and soft repeaters(which may not always be visible on a die). If only a limited number ofdies are imaged, it can be challenging to detect repeater defects andcan be especially challenging to detect soft repeaters.

In an instance, a first wafer can be inspected and/or recorded at t=0 todetect and/or record systematic nuisance on a reticle. This can be partof an integrated solution for EUV mask inspection. At t>0 (e.g., threeweeks later), a second wafer can be inspected and/or recorded.Systematic nuisance in t>0 can be subtracted from t=0. Random reticledefects can be reported. This can provide a lower nuisance rate and,thus, higher sensitivity to DOI. For example, t=0 can be when thereticle is clean and/or problem-free and t>0 can mean that there areparticles on and/or other problems with the reticle. These otherproblems may be caused by misalignment during printing or reticledefects.

FIG. 3 is a first embodiment of nuisance reduction. A first die and asecond die are each imaged using a reticle at two different positions(reticle1, reticle2) on a first wafer (t=0) and two different positions(reticle1, reticle2) on a second wafer (t>0). The two differentpositions may be, for example, different rows on the wafer. The firstdie and the second die may be neighboring dies or may have other spatialrelationships. The image processing steps may be performed by aprocessor.

A first wafer difference image is calculated. To do so, a differenceimage of the first die and the second die at a second position on thefirst wafer is calculated. A difference image of the first die at thesecond position on the first wafer and the second die at a firstposition on the first wafer also is calculated. Then the first waferdifference image is calculated from the two resulting difference images.

A second wafer difference image is calculated. To do so, a differenceimage of the first die and the second die at a second position on thesecond wafer is calculated. A difference image of the first die at thesecond position on the first wafer and the second die at a firstposition on the second wafer also is calculated. Then the second waferdifference image is calculated from the two resulting difference images.

Systematic defects in the first difference image can be found usingcoordinate-based defect source analysis. The systematic defects in thefirst wafer difference image can be subtracted from the second waferdifference image based on their coordinates. Existence of a DOI in thesecond wafer difference image can be determined after the common (e.g.,systematic) defects have been excluded.

FIG. 4 is a second embodiment of nuisance reduction. A first die and asecond die are each imaged using a reticle at two different positions(reticle1, reticle2) on a first wafer (t=0) and two different positions(reticle1, reticle2) on a second wafer (t>0). The two differentpositions may be, for example, different rows on the wafer. The firstdie and the second die may be neighboring dies or may have other spatialrelationships. The image processing steps may be performed by aprocessor.

A difference image of the first die and the second die at a secondposition on the second wafer is calculated. A difference image of thefirst die at the second position on the first wafer and the second dieat a first position on the second wafer is calculated. Then a waferdifference image is calculated from the two resulting difference images.

Existence of a defect of interest in the wafer difference image isdetermined. Images can be retrieved from the storage medium. The imagesare at the same location on the first wafer (e.g., t=0) as the first dieand the second die on the second wafer that were used in thecalculating.

Presence of the defect of interest can be evaluated in the images fromthe storage medium. Nuisance can be filtered from the wafer differenceimage.

FIG. 5 is a third embodiment of nuisance reduction. A first die and asecond die are each imaged using a reticle at two different positions(reticle1, reticle2) on a first wafer (t=0) and two different positions(reticle1, reticle2) on a second wafer (t>0). The two differentpositions may be, for example, different rows on the wafer. The firstdie and the second die may be neighboring dies or may have other spatialrelationships. The image processing steps may be performed by aprocessor.

A first wafer difference image is calculated. To do so, a differenceimage of the first die and the second die at a second position on thefirst wafer is calculated. A difference image of the first die at thesecond position on the first wafer and the second die at a firstposition on the first wafer also is calculated. Then the first waferdifference image is calculated from the two resulting difference images.

A second wafer difference image is calculated. To do so, a differenceimage of the first die and the second die at a second position on thesecond wafer is calculated. A difference image of the first die at thesecond position on the first wafer and the second die at a firstposition on the second wafer also is calculated. Then the second waferdifference image is calculated from the two resulting difference images.

The second wafer difference image is subtracted from the first waferdifference image. Existence of a defect of interest in the second waferdifference image can be determined after the subtracting.

FIG. 2 is a system drawing of a system 300. The system 300 includes awafer inspection tool 301 and a controller 303 with a processor 304 andan electronic data storage unit 305 in electronic communication with theprocessor 304. The wafer inspection tool 301 may be a BBP tool, whichcan be configured to perform a hot scan to capture inspection results.The wafer inspection tool also may be a laser scanning tool, an electronbeam inspector, or other inspection systems. The controller 303 is inelectronic communication with the wafer inspection tool 301.

The controller 303 may be part of the wafer inspection tool 301, oranother device. In an example, the controller 303 may be a standalonecontrol unit or in a centralized quality control unit. Multiplecontrollers 303 may be used.

The controller 303 may be implemented in practice by any combination ofhardware, software, and firmware. Also, its functions as describedherein may be performed by one unit, or divided up among differentcomponents, each of which may be implemented in turn by any combinationof hardware, software and firmware. Program code or instructions for thecontroller 303 to implement various methods and functions may be storedin controller readable storage media, such as a memory in the electronicdata storage unit 305 or other memory.

The controller 303 may be coupled to the components of the system 300 inany suitable manner (e.g., via one or more transmission media, which mayinclude wired and/or wireless transmission media) such that thecontroller 303 can receive the output generated by the system 300. Thecontroller 303 may be configured to perform a number of functions usingthe output.

The controller 303, other system(s), or other subsystem(s) describedherein may be part of various systems, including a personal computersystem, image computer, mainframe computer system, workstation, networkappliance, internet appliance, or other device. The subsystem(s) orsystem(s) may also include any suitable processor known in the art, suchas a parallel processor. In addition, the subsystem(s) or system(s) mayinclude a platform with high speed processing and software, either as astandalone or a networked tool.

If the system includes more than one subsystem, then the differentsubsystems may be coupled to each other such that images, data,information, instructions, etc. can be sent between the subsystems. Forexample, one subsystem may be coupled to additional subsystem(s) by anysuitable transmission media, which may include any suitable wired and/orwireless transmission media known in the art. Two or more of suchsubsystems may also be effectively coupled by a shared computer-readablestorage medium (not shown).

An additional embodiment relates to a non-transitory computer-readablemedium storing program instructions executable on a controller forperforming a computer-implemented defect detection or wafer inspection,as disclosed herein. In particular, the processor 304 can be coupled toa memory in the electronic data storage unit 305 or other electronicdata storage medium with non-transitory computer-readable medium thatincludes program instructions executable on the processor 304. Thecomputer-implemented method may include any step(s) of any method(s)described herein. For example, the controller 303 may be programmed toperform some or all of the steps of FIG. 1, FIGS. 3-5, or otherembodiments disclosed herein, which can be executed by the processor304. The memory in the electronic data storage unit 305 or otherelectronic data storage medium may be a storage medium such as amagnetic or optical disk, a magnetic tape, or any other suitablenon-transitory computer-readable medium known in the art. In particular,the electronic data storage unit can include persistent storage, randomaccess memory, or a split database.

The program instructions may be implemented in any of various ways,including procedure-based techniques, component-based techniques, and/orobject-oriented techniques, among others. For example, the programinstructions may be implemented using ActiveX controls, C++ objects,JavaBeans, Microsoft Foundation Classes (MFC), SSE (Streaming SIMDExtension), or other technologies or methodologies, as desired.

As used herein, the term “wafer” generally refers to substrates formedof a semiconductor or non-semiconductor material. Examples of such asemiconductor or non-semiconductor material include, but are not limitedto, monocrystalline silicon, gallium arsenide, and indium phosphide.Such substrates may be commonly found and/or processed in semiconductorfabrication facilities.

A wafer may include one or more layers formed upon a substrate. Forexample, such layers may include, but are not limited to, a resist, adielectric material, and a conductive material. Many different types ofsuch layers are known in the art, and the term wafer as used herein isintended to encompass a wafer including all types of such layers.

One or more layers formed on a wafer may be patterned or unpatterned.For example, a wafer may include a plurality of dies, each havingrepeatable patterned features. Formation and processing of such layersof material may ultimately result in completed devices. Many differenttypes of devices such as integrated circuits may be formed on a wafer,and the term wafer as used herein is intended to encompass a wafer onwhich any type of device known in the art is being fabricated. As usedherein, the term “chip” may comprise a collection of integrated circuitsdesigned for a particular purpose.

Although embodiments are described herein with respect to wafers, it isto be understood that the embodiments may be used for another specimensuch as a reticle, which may also be commonly referred to as a mask or aphotomask. Many different types of reticles are known in the art, andthe terms “reticle,” “mask,” and “photomask” as used herein are intendedto encompass all types of reticles known in the art.

Each of the steps of the method may be performed as described herein.The methods also may include any other step(s) that can be performed bythe controller and/or computer subsystem(s) or system(s) describedherein. The steps can be performed by one or more computer systems,which may be configured according to any of the embodiments describedherein. In addition, the methods described above may be performed by anyof the system embodiments described herein.

Although the present disclosure has been described with respect to oneor more particular embodiments, it will be understood that otherembodiments of the present disclosure may be made without departing fromthe scope of the present disclosure. Hence, the present disclosure isdeemed limited only by the appended claims and the reasonableinterpretation thereof.

What is claimed is:
 1. A method to detect repeater defects comprising:performing a hot scan inspection of an entire surface of a wafer;storing a position of defects from the hot scan inspection to a storagemedium, wherein the storage medium is persistent storage, random accessmemory, or a split database; determining, using a processor, coordinatesfor repeater defect detection; inspecting the wafer based on thecoordinates for repeater defect detection; analyzing repeater defectsusing the processor; and retrieving corresponding defect records to therepeater defects from the storage medium.
 2. The method of claim 1,wherein a patch-based virtual inspector virtual analyzer is used for thestorage medium
 3. The method of claim 1, wherein local storage is usedfor the storage medium.
 4. The method of claim 1, further comprisingfreeing space in the storage medium after the retrieving.
 5. The methodof claim 1, further comprising saving coordinates of the defects inshared memory prior to the determining.
 6. The method of claim 1,wherein a first die and a second die are each imaged using a reticle attwo different positions on a first wafer and two different positions ona second wafer, further comprising: calculating a first wafer differenceimage in a first wafer step by: calculating, using the processor, adifference image of the first die and the second die at a secondposition on the first wafer; calculating, using the processor, adifference image of the first die at the second position on the firstwafer and the second die at a first position on the first wafer; andcalculating, using the processor, the first wafer difference image ofthe two difference images of the first wafer step; calculating a secondwafer difference image in a second wafer step by: calculating, using theprocessor, a difference image of the first die and the second die at asecond position on the second wafer; calculating, using the processor, adifference image of the first die at the second position on the firstwafer and the second die at a first position on the second wafer; andcalculating, using the processor, the second wafer difference image ofthe two difference images of the second wafer step; finding, using theprocessor, systematic defects in the first wafer difference image usingcoordinate-based defect source analysis; subtracting, using theprocessor, the systematic defects in the first wafer difference imagefrom the second wafer difference image; and determining, using theprocessor, existence of a defect of interest in the second waferdifference image after the subtracting.
 7. The method of claim 1,wherein a first die and a second die are each imaged using a reticle attwo different positions on a first wafer and two different positions ona second wafer, further comprising: calculating a first wafer differenceimage in a first wafer step by: calculating, using the processor, adifference image of the first die and the second die at a secondposition on the first wafer; calculating, using the processor, adifference image of the first die at the second position on the firstwafer and the second die at a first position on the first wafer; andcalculating, using the processor, the first wafer difference image ofthe two difference images of the first wafer step; calculating a secondwafer difference image in a second wafer step by: calculating, using theprocessor, a difference image of the first die and the second die at asecond position on the second wafer; calculating, using the processor, adifference image of the first die at the second position on the firstwafer and the second die at a first position on the second wafer; andcalculating, using the processor, the second wafer difference image ofthe two difference images of the second wafer step; subtracting, usingthe processor, the second wafer difference image from the first waferdifference image; and determining, using the processor, existence of adefect of interest in the second wafer difference image after thesubtracting.
 8. The method of claim 1, wherein a first die and a seconddie are each imaged using a reticle at two different positions on afirst wafer and two different positions on a second wafer, furthercomprising: calculating a wafer difference image by: calculating, usingthe processor, a difference image of the first die and the second die ata second position on the second wafer; calculating, using the processor,a difference image of the first die at the second position on the firstwafer and the second die at a first position on the second wafer; andcalculating, using the processor, the wafer difference image of the tworesulting difference images; determining, using the processor, existenceof a defect of interest in the wafer difference image; retrieving imagesfrom the storage medium, wherein the images are at a same location onthe first wafer as the first die and the second die on the second wafer;evaluating, using the processor, presence of the defect of interest inthe images from the storage medium; and filtering, using the processor,nuisance from the wafer difference image.
 9. A method for filteringnuisance comprising: imaging a first die and a second die using areticle at two different positions on a first wafer and two differentpositions on a second wafer; calculating a difference image of thesecond wafer in a second wafer step by: calculating, using a processor,a difference image of the first die and the second die at a secondposition on the second wafer; calculating, using the processor, adifference image of the first die at the second position on the firstwafer and the second die at a first position on the second wafer; andcalculating, using the processor, the difference image of the secondwafer using the two difference images of the second wafer step; anddetermining, using the processor, existence of a defect of interest inthe wafer difference image of the second wafer.
 10. The method of claim9, further comprising: retrieving images from the storage medium,wherein the images are at a same location on the first wafer as thefirst die and the second die on the second wafer; evaluating, using theprocessor, presence of the defect of interest in the images from thestorage medium; and filtering, using the processor, nuisance from thesecond wafer difference image.
 11. The method of claim 9, furthercomprising: calculating a difference image of the first wafer in a firstwafer step by: calculating, using the processor, a difference image ofthe first die and the second die at a second position on the firstwafer; calculating, using the processor, a difference image of the firstdie at the second position on the first wafer and the second die at afirst position on the first wafer; and calculating, using the processor,the wafer difference image of the first wafer using the two differenceimages of the first wafer step; finding, using the processor, systematicdefects in the difference image of the first wafer usingcoordinate-based defect source analysis; and subtracting, using theprocessor, the systematic defects in the difference image of the firstwafer from the difference image of the second wafer, wherein thedetermining existence of the defect of interest in the difference imageof the second wafer is after the subtracting.
 12. The method of claim 9,further comprising: calculating a difference image of the first wafer ina first wafer step by: calculating, using the processor, a differenceimage of the first die and the second die at a second position on thefirst wafer; calculating, using the processor, a difference image of thefirst die at the second position on the first wafer and the second dieat a first position on the first wafer; and calculating, using theprocessor, the difference image of the first wafer using the twodifference images of the first wafer step; and subtracting, using theprocessor, the difference image of the second wafer from the differenceimage of the first wafer, wherein the determining existence of thedefect of interest in the difference image of the second wafer is afterthe subtracting.
 13. A system comprising: a controller in electroniccommunication with a wafer inspection tool, wherein the controllerincludes a processor and an electronic data storage unit in electroniccommunication with the processor, wherein the electronic data storageunit includes persistent storage, random access memory, or a splitdatabase, and wherein the controller is configured to: receive resultsof a hot scan inspection of an entire surface of a wafer from the waferinspection tool; store a position of defects from the hot scaninspection to the electronic data storage unit; determine coordinatesfor repeater defect detection; send instructions to inspect the waferbased on the coordinates for repeater defect detection; analyze repeaterdefects; and retrieve corresponding defect records to the repeaterdefects from the electronic data storage unit.
 14. The system of claim13, wherein the electronic data storage unit is included in apatch-based virtual inspector virtual analyzer.
 15. The system of claim13, wherein the electronic data storage unit is local storage.
 16. Thesystem of claim 13, wherein the controller is configured to savecoordinates of the defects in shared memory prior to determine therepeater defect detection jobs.
 17. The system of claim 13, wherein afirst die and a second die are each imaged using a reticle at twodifferent positions on a first wafer and two different positions on asecond wafer, wherein the controller is further configured to: calculatea first wafer difference image in a first wafer step by: calculating adifference image of the first die and the second die at a secondposition on the first wafer; calculating a difference image of the firstdie at the second position on the first wafer and the second die at afirst position on the first wafer; and calculating the first waferdifference image of the resulting difference images of the first waferstep; calculate a second wafer difference image in a second wafer stepby: calculating a difference image of the first die and the second dieat a second position on the second wafer; calculating a difference imageof the first die at the second position on the first wafer and thesecond die at a first position on the second wafer; and calculating thesecond wafer difference image of the resulting difference images of thesecond wafer step; find systematic defects in the first wafer differenceimage using coordinate-based defect source analysis; subtract thesystematic defects in the first wafer difference image from the secondwafer difference image; and determine existence of a defect of interestin the second wafer difference image after the subtracting.
 18. Thesystem of claim 13, wherein a first die and a second die are each imagedusing a reticle at two different positions on a first wafer and twodifferent positions on a second wafer, wherein the controller is furtherconfigured to: calculate a first wafer difference image in a first waferstep by: calculating a difference image of the first die and the seconddie at a second position on the first wafer; calculating a differenceimage of the first die at the second position on the first wafer and thesecond die at a first position on the first wafer; and calculating thefirst wafer difference image of the resulting difference images of thefirst wafer step; calculate a second wafer difference image in a secondwafer step by: calculating a difference image of the first die and thesecond die at a second position on the second wafer; calculating adifference image of the first die at the second position on the firstwafer and the second die at a first position on the second wafer; andcalculating the second wafer difference image of the resultingdifference images of the second wafer step; subtract the second waferdifference image from the first wafer difference image; and determineexistence of a defect of interest in the second wafer difference imageafter the subtracting.
 19. The system of claim 13, wherein a first dieand a second die are each imaged using a reticle at two differentpositions on a first wafer and two different positions on a secondwafer, wherein the controller is further configured to: calculate awafer difference image by: calculating a difference image of the firstdie and the second die at a second position on the second wafer;calculating a difference image of the first die at the second positionon the first wafer and the second die at a first position on the secondwafer; and calculating the wafer difference image of the resultingdifference images; determine existence of a defect of interest in thesecond wafer difference image; retrieve images from the electronic datastorage unit, wherein the images are at a same location on the firstwafer as the first die and the second die on the second wafer; evaluatepresence of the defect of interest in the images from the electronicdata storage unit; and filter nuisance from the wafer difference image.